Response of water vapour D-excess to land–atmosphere interactions in a semi-arid environment

Abstract

Abstract. The stable isotopic composition of water vapour provides information about moisture sources and processes difficult to obtain with traditional measurement techniques. Recently, it has been proposed that the D-excess of water vapour (dv = δ2H − 8 × δ18O) can provide a diagnostic tracer of continental moisture recycling. However, D-excess exhibits a diurnal cycle that has been observed across a variety of ecosystems and may be influenced by a range of processes beyond regional-scale moisture recycling, including local evaporation (ET) fluxes. There is a lack of measurements of D-excess in evaporation (ET) fluxes, which has made it difficult to assess how ET fluxes modify the D-excess in water vapour (dv). With this in mind, we employed a chamber-based approach to directly measure D-excess in ET (dET) fluxes. We show that ET fluxes imposed a negative forcing on the ambient vapour and could not explain the higher daytime dv values. The low dET observed here was sourced from a soil water pool that had undergone an extended drying period, leading to low D-excess in the soil moisture pool. A strong correlation between daytime dv and locally measured relative humidity was consistent with an oceanic moisture source, suggesting that remote hydrological processes were the major contributor to daytime dv variability. During the early evening, ET fluxes into a shallow nocturnal inversion layer caused a lowering of dv values near the surface. In addition, transient mixing of vapour with a higher D-excess from above the nocturnal inversion modified these values, causing large variability during the night. These results indicate d

Water fluxes mediated by vegetation: emerging isotopic insights at the soil and atmosphere interfaces

“…Moreover, the impact of ET on water vapour in the planetary boundary layer, quantified in high temporal resolution (i.e. hours), facilitates predictions of enhanced regional precipitation recycling (Griffis, 2013;Griffis et al, 2016;Parkes et al, 2016). We anticipate a significant increase of investigations quantifying the dynamic interaction between vegetation and atmospheric moisture exchange and its feedback on both vegetation functioning and synoptic processes, which are important components buffering or enhancing alterations in the global water cycle induced by climate change.…”

Assessing moisture sources of precipitation in the Western Pamir Mountains (Tajikistan, Central Asia) using deuterium excess

“…These theoretical basics enable applications to estimate contributions of recycled inland water to precipitation (Froehlich et al, 2008;Aemisegger et al, 2014;Parkes et al, 2017). They may also discern and compare meteorological patterns (Liotta et al, 2006;Guan et al, 2013), and enable the paleoclimate interpretation of ice cores (Jouzel et al, 1982;Steffensen et al, 2008).…”

Novel Keeling-plot-based methods to estimate the isotopic composition of ambient water vapor

“…The f ET estimate will provide a baseline value for rainfall recycling ratio calculations. Previous studies quantified the contribution of recycled vapor to annual or monthly precipitation in river basins using a two-element mixture model (Kong et al, 2013) and three-element mixture (Peng et al, 2011). At the watershed scale, the recycled vapor rate refers to the contributions of moisture from terrestrial ET to annual or monthly precipitation (Trenberth, 1999).…”